The present invention relates to medical diagnosis, treatment and imaging systems. More particularly, the present invention relates to medical probes whose location can be detected and adjusted and which have an additional detection, imaging and/or treatment function.
Probes, such as catheters, suitable for various medical procedures and internal imaging, are fairly common. Such probes include: balloon angioplasty, catheters, catheters with laser-, electrical- or cryo-ablation characteristics, catheters having ultrasound imaging heads, probes used for nearly incisionless-surgery or diagnosis, and endoscopes. Where such probes are used for treatment, the probes must be carefully positioned in relation to the body structure. Even for imaging systems such as ultrasound systems, some positioning capability has been described.
In cardiovascular examinations and in particular in those using invasive techniques, multiple catheters are inserted into the vascular system and then advanced towards the cardiac chambers. The procedure itself is generally performed under fluoroscope guidance which necessitates the use of a continuous source of x-ray as a transillumination source. The image generated using the fluoroscope is a 2D display of the anatomy with the location of the catheter superimposed. The anatomy can be viewed with a relatively low resolution since the cardiac chamber and the blood vessels are transparent to the x-ray radiation.
More recently, several technologies have been developed to ease the process of cardiac catheterization, mainly by enabling the physician to follow the path of the tip of the catheter inside the blood vessel. Some of this technology is based on digital subtraction radiography technology that enables viewing the blood vessel after the injection of a radio contrast dye and superimposing on that image the path of the catheter. These technologies necessitate the use of radiopaque dyes which are a major cause of morbidity in high-risk patients during cardiac catheterization.
U.S. Pat. No. 5,042,486 to Pfeiller et al., the disclosure of which is incorporated herein by reference, describes a method in which the position of a catheter tip is located using electromagnetic fields. The catheter is introduced and the tip location is followed. The path of the tip is superimposed on the pre-registered image of the blood vessel or the organ, through which the catheter was advanced. However, this technology requires acquisition and processing of images prior to the procedure and involves a highly sophisticated and time-consuming procedure for the correct alignment of the image acquired previous to this procedure, and the orientation and location of the blood vessel or the organ during the catheterization procedure itself.
U.S. Pat. No. 4,821,731 to Martinelli et al., the disclosure of which is incorporated herein by reference, discloses a method for internal imaging of a living body using ultrasound. In this patent the position of an ultrasound imaging catheter is determined by computing the relative position of the catheter using the response of an ultrasound transducer to a reference signal, and by computing the angular orientation of the catheter about its axis by determining the signal induced in a single coil by substantially perpendicular magnetic fields of different frequencies. The ultrasound transducer is also used to send and detect ultrasound signals in a direction perpendicular to the catheter axis. By rotating the catheter and moving it along its axis an ultrasound image may be generated. The catheter is also described as being capable of transmitting a laser beam to the end thereof to ablate tissue from lesions on the walls of arteries.
A catheter which can be located in a patient using an ultrasound transmitter located in the catheter, is disclosed in U.S. Pat. No. 4,697,595 and in the technical note xe2x80x9cUltrasonically Marked Catheter, a Method for Positive Echographic Catheter Position and Identificationxe2x80x9d, Bryer et al., Medical and Biological Engineering and Computing, May, 1985, pages 268-271. Also, U.S. Pat. No. 5,042,486 discloses a catheter which can be located in patients using non-ionizing fields and suitably imposing catheter location on a previously obtained radiological image of the blood vessel.
PCT Patent Publication WO 94/0938, the disclosure of which is incorporated herein by reference, describes a system using a single-coil type sensor which is coaxial with the long axis of a catheter and which senses fields which are generated by three multicoil generators external to the body of a patient.
Other methods and apparatus for the determination of the position of a catheter or endoscope are shown in U.S. Pat. Nos. 5,253,647; 5,057,095; 4,095,698; 5,318,025; 5,271,400; 5,211,165; 5,265,610; 5,255,680; 5,251,635 and 5,265,611.
U.S. Pat. No. 3,644,825 describes a system which uses the relative motion of a sensor in the determination of its position. The relative motion supplies information to the sensing coils needed to identify position and orientation. However, such a solution is not applicable to identifying position and location of the object where there is no relative motion between the object and the reference frame.
U.S. Pat. No. 3,868,565, the disclosure of which is incorporated herein by reference, comprises a tracking system for continuously determining the relative position and orientation of a remote object. This tracking system includes orthogonally positioned loops for both a plurality of sensors and a plurality of radiating antennas. With the proper excitation currents to those loops, the radiating antennas generate an electromagnetic field that is radiated from those antennas to the sensor. The tracking system operates as a closed loop system where a controlling means measures the field that is received at the sensor at the remote object and feeds the information back to radiating antennas to provide a nutating field radiating as a pointing vector towards the remote object. Accordingly, the pointing vector gives the direction to the sensing antenna from the radiating antenna.
Similarly, Kuipers describes in his U.S. Pat. No. 4,017,858, the disclosure of which is incorporated herein by reference, an electromagnetic field which rotates about a pointing vector and is used both to track or locate the remote object in addition to determining the relative orientation of the object. This system, wherein the radiating coils are charged with the properly designed wave forms, generates a magnetic field which, in a closed loop manner, can be fed into processing means to generate the information needed to determine an orientation of a remote object.
U.S. Pat. No. 4,054,881, the disclosure of which is incorporated herein by reference, describes a non-tracking system for determining the position and location of a remote object with respect to a reference frame. This is accomplished by applying electrical signals to each of three mutually-orthogonal, radiating antennas, the electrical signals being multiplexed with respect to each other and containing information characterizing the polarity and magnetic moment of the radiated electromagnetic fields. The radiated fields are detected and measured by the three mutually orthogonal receiving antennas having a known relationship to the remote object, which produce nine parameters. These nine parameters, in combination with one known position or orientation parameter, are sufficient to determine the position and orientation parameters of the receiving antennas with respect to the position and orientation of the radiating antennas.
U.S. Pat. No. 4,849,692, the disclosure of which is incorporated herein by reference, describes a quantitative method for measuring the relative position and orientation of two bodies in the presence of metals. Measuring the position and orientation of receiving antennas with respect to the transmitting antennas is achieved using direct current electromagnetic field signals. Electromagnetic radiation is designed to be transmitted in a sequence by each of the mutually orthogonal radiating antennas. A receiving antenna measures the values of transmitted direct current magnetic fields, one dimension at a time, and those of the earth""s magnetic field as well. This method requires repetitive acquisition and computations to determine position and location of remote objects.
Other methods which are known in the art for determining multi-dimensional positioning and orientation for aircraft and for helmets are described in U.S. Pat. No. 4,849,692, European patent publication 0 576 187 A1, GB patent publication 2 197 078 A and U.S. Pat. No. 4,314,251 the disclosures of which are incorporated herein by reference.
The above described prior art which is for use in non-medical applications, utilizes sensors and other structures which are not suitable for use in catheters. Those references which are described as being useful for medical probes generally give less than six dimensional information (three position coordinates and three angular coordinates).
In previous, as yet unpublished applications assigned to the assignee of the present application, U.S. patent application Ser. No. 08/094,539, filed Jul. 20, 1993 and PCT Application PCT/US94/08352 filed Jul. 20, 1994, the disclosures of which are incorporated herein by reference, a system is disclosed which incorporates a catheter which includes a position measuring device which can determine the position of the catheter in three dimensions, but not its orientation. In these applications, this catheter is used to map the electrical activity at the inner walls of the heart and to ablate portions of the heart muscle in response to such mappings. The position of the catheter used for the mapping/ablation function is determined with reference to three position detecting devices which are positioned against the inner wall of the heart at three different stable locations to form a reference plane.
In general the present application discloses a catheter locating means and method that offers quantitative, high resolution locating information that, when assimilated with sensed local information results in a high resolution, detailed map of the information. This map may optionally be superimposed on an image or other representation of the organ architecture.
The locating means preferably generates continuous location and orientation information concerning a remote object, in particular a catheter, relative to a reference frame, in a non-iterative manner.
One aspect of the present invention relates to the provision of a new six-dimensional positioning apparatus suitable for use with a catheter.
In a preferred embodiment of this system, a plurality of non-concentric coils are placed in a catheter adjacent a locatable site; for example, its distal end. The coils preferably have orthogonal axis. The relative positioning of the coils differs from that described in the prior art in that the coils are separated in space and are not concentric. These coils generate signals in response to externally applied magnetic fields which allows for the computation of six position and orientation dimensions.
A second aspect of the present invention is directed toward a new method for computing multi-dimensional position and orientation of a coil system from signals produced by the coils in response to a system of externally applied electromagnetic fields.
A third aspect of the present invention allows for the mapping of the interior of the heart in a manner similar to that described in the above-referenced patent applications assigned to the assignee of the present application, with the simplification that only a single six-dimensional location/orientation detection sensor is used for reference.
A fourth aspect of the present invention involves an ultrasonic or other imaging probe having a six-dimensional positioning capability in response to external electromagnetic fields. Use of such a probe obviates the use of ionizing radiation or sonic sensing for position determination and gives ultrasonic or other imaging information whose direction and orientation is completely known.
A fifth aspect of the invention involves methods and apparatus for adding a controlled change in orientation to a catheter, thereby to allow for maneuvering of the cathode and its easy placement.
A sixth aspect of the invention utilizes the controlled change in orientation to allow for two or three-dimensional imaging using a non-scanning probe, such as an ultrasound probe or for three-dimensional scanning using a two-dimensional scanning probe.
There is therefore provided, in accordance with a preferred embodiment of the invention, a locating system for determining the location and orientation of an invasive medical instrument, for example a catheter or endoscope, relative to a reference frame, comprising:
a plurality of field generators which generate known, distinguishable fields, preferably continuous AC magnetic fields, in response to drive signals;
a plurality of sensors situated in the invasive medical instrument proximate the distal end thereof which generate sensor signals in response to said fields; and
a signal processor which has an input for a plurality of signals corresponding to said drive signals and said sensor signals and which produces the three location coordinates and three orientation coordinates of a point on the invasive medical instrument.
Preferably one or both of the plurality of field generators or sensors comprises three distinguishable, non-overlapping, generators or sensors.
In a preferred embodiment of the invention, each sensor comprises a coil. Preferably, said plurality of coils have axes which intersect within a coil. When said plurality of coils comprises three coils, said coils preferably have axes which do not all intersect in a point.
Preferably, the signal processor cross-correlates the signals corresponding to the drive and sensor signals.
Preferably, the fields generated by each of the generators have a different frequency, a different phase, or both a different frequency and a different phase.
In a preferred embodiment of the invention the field generated by each field generator has a different frequency, preferably frequencies which are each integer multiples of a given frequency. Preferably, the duration of the cross-correlation of the inputs is the minimal common product of the integer multipliers divided by the given frequency.
Preferably, the results of the cross-correlation are used to calculate the contribution of each field generator to the signal generated by each said sensor.
In a preferred embodiment of the invention the locating system includes a display system for displaying the position of the point on the invasive medical instrument.
Preferably, the locating system further comprises a reference instrument which includes a plurality of non-overlapping sensors situated in the reference instrument which sensors generate sensor signals in response to said fields, wherein said display system displays the position of the point on the invasive medical instrument relative to the position of a point on the reference instrument. Preferably the reference instrument is an invasive medical instrument. Preferably, the sensors are situated proximate the distal end of the reference invasive medical instrument.
In a preferred embodiment of the invention the locating system includes an additional sensor on a portion of the invasive medical instrument which senses a local condition.
Preferably, the additional sensor senses local electrical signals, for example electrical signals from the endocardium of the patient""s heart, and transfers them to terminals external to the patient""s body.
In a preferred embodiment of the invention the signal processor processes the position and orientation coordinate signals and the local electrical signals acquired at a plurality of points on the endocardium to generate a map that represents the propagation of electrical signals through tissue in the patient""s body.
In a preferred embodiment of the invention the additional sensor supplies electrical energy to the endocardium for ablating a portion of the endocardium.
Preferably the locating system includes an electrode adapted for supplying electrical energy to the endocardium for ablating a portion of the endocardium.
In a preferred embodiment of the invention the additional sensor is an ultrasonic transmitter/receiver.
Preferably, the ultrasonic transmitter/receiver provides a less than three dimensional representation of the acoustic properties of tissue beyond the distal end.
In a preferred embodiment of the invention, the distal end is deflectable. Preferably, the system includes image reconstruction circuitry which receives a plurality of said less than three dimensional representations acquired at different orientations of the distal end and produces a three dimensional map of the acoustic properties of tissue at least partially surrounding the distal end.
There is further provided, in accordance with a preferred embodiment of the invention, an imaging system for intrabody ultrasonic imaging comprising:
a invasive medical instrument, preferably, a catheter or endoscope, having an axial-looking ultrasonic imaging transducer at the distal end thereof which generated a representation, preferably a one or two dimensional representation, of the acoustic properties of tissue beyond the distal end;
means for manipulating the distal end to change the orientation thereof; and
image reconstruction circuitry which receives a plurality of said representations acquired at different orientations of the distal end and produces a three dimensional map of the acoustic properties of tissue at least partially surrounding the distal end from said plurality of representations.
Preferably, the imaging system further comprises:
a plurality of field generators which generate known, distinguishable fields in response to drive signals;
a plurality of sensors situated in the invasive medical instrument proximate the distal end thereof which generate sensor signals in response to said fields; and
a signal processor which has an input for a plurality of signals corresponding to said drive signals and said sensor signals and which produces three location coordinates and three orientation coordinates of the a point on the transducer.
There is further provided a method of determining the position and orientation of an invasive medical instrument, for example a catheter or endoscope, having a distal end, comprising:
(a) generating a plurality, preferably three, of distinguishable, geometrically different AC magnetic fields;
(b) sensing the AC magnetic fields at the sensors at a plurality of points proximate the distal end; and
(c) computing six dimensions of position and orientation of a portion of the invasive medical instrument responsive to signals representative of the generated magnetic fields and the sensed magnetic fields.
Preferably, the AC magnetic field is sensed at three points of the invasive medical instrument.
There is further provided, in accordance with a preferred embodiment of the invention, an ultrasonic intrabody imaging method comprising:
(a) inserting an ultrasonic transducer into the body, said ultrasonic transducer producing a representation of the acoustic properties of tissue beyond an end of the transducer;
(b) manipulating the orientation of the transducer to provide a plurality of said representations; and
(c) constructing a three dimensional map of the acoustic properties of the tissue in a region at least partially surrounding the end of the transducer from said plurality of representations.
Preferably, the method includes determining the six dimensions of position and orientation of the transducer for each of the representations.
Preferably, the representation is a less than three dimensional representation.
There is further provided an invasive medical instrument, for example a catheter or endoscope, comprising a plurality of magnetic field sensors, preferably coils, proximate the distal end thereof.
Preferably the plurality of coils have axes which intersect within a coil. Where the plurality is three, the said coils have axes which do not all intersect in a point.
In a preferred embodiment of the invention, the instrument comprises an ultrasound transducer at said distal end. Preferably, the ultrasound transducer provides a representation, preferably a one or two dimensional representation, of the acoustic properties of tissue beyond and along the axis of the catheter.
In a preferred embodiment of the invention, the instrument further comprises an electrical probe at said distal end. The probe is preferably adapted to sense electrical signals generated by tissue which is in contact and conduct said signals to the proximal end of the catheter and/or to supply an ablative electrical signal to tissue contacting said terminal. In a preferred embodiment of the invention, the instrument includes a sensor for measuring local chemistry at the distal end.
Preferably, the instrument includes means for changing the orientation of the distal end.
There is further provided, in accordance with a preferred embodiment of the invention, apparatus for steering the distal end of an invasive medical instrument, such as a catheter or endoscope, comprising:
a relatively more flexible wire passing through the catheter that is attached to the distal end and has a bend near the distal end;
a relatively more rigid sleeve which is straight near the distal end and which slideably holds the wire thereat, whereby when the sleeve is slid over the wire, the wire and distal end are straightened.
Preferably, the instrument has a lengthwise axis and the wire is sited off the axis of the instrument.
There is further provided apparatus for steering the distal end of an invasive medical instrument comprising:
a flat relatively flexible portion being slit along a portion of the length thereof to form two portions which are attached at a first end thereof, said first end being attached to the distal end of the instrument;
a pair of wires, one end of each of which being attached to one of said portions at a second end thereof; and
means for changing the relative lengths of the wires whereby the flexible element is bent, thereby steering the distal end of the instrument.
There is further provided, in accordance with a preferred embodiment of the invention, a method of producing a three dimensional image of the internal surface of an internal body organ comprising:
measuring the distance to said surface at a plurality of orientations from within the internal surface; and
assembling the distances to form an image of the surface.
Preferably, the measurement of distances is made from a plurality of points within the organ. Preferably, the measurement of distances is preformed utilizing an ultrasonic transducer.